Strip scheduling condition nodes.
The Windows Installer parser for conditions does not like leading or trailing spaces. This means that fairly common constructs like
<Custom Action='dostuff' After='InstallServices'>
(NOT Installed) AND (NOT REMOVE)
</Custom>
will have the "wrong" condition (NOT Installed) AND (NOT REMOVE)
,
leading to the windows installer framework raising an error when
executing the action.
To avoid this, we simply strip the leading and trailing spaces of conditions.